Annunciator system

ABSTRACT

An annunciator system of the type having a central annunciating station and remote receptacles typically adapted for receipt of a plug-in manual controller, not requiring power for operation thereof, is improved by introduction of a controller adapted to monitor changing conditions. The introduced controller is a plugin unit deriving all required operating power through the remote receptacle and at the same time providing system control inputs through the receptacle. The introduced controller may also have facility for receiving the manual controller to provide the annunciator system with plural inputs. units. In a preferred arrangement, the system is shown in hospital usage where it provides for the monitoring of a liquid level.

Unite States Patent 1 Geller et al.

[5 ANNUNCIATOR SYSTEM Primary Examiner-Thomas B. Habecker [76] Inventors: Martin R. Geller, 318 East 19th Helfench Street, New York, NY. 10013; David A. Goldman, Corton Heights [57] ABSTRACT BOX 691 Yorktown An annunciator system of the type having a central Helghts 10598 annunciating station and remote receptacles typically 22 Filed; Sept 7 1971 adapted for receipt of a plug-in manual controller, not requiring power for operation thereof, is improved by [21] Appl 178244 introduction of a controller adapted to monitor changing conditions. The introduced controller is a plug-in [52] US. Cl. ..340/244 C, 340/279 unit deriving all required operating power through the [51] Int.Cl. ..G08b 21/00 remote receptacle and at the same time providing of Search C system control inputs through the receptacle The introduced controller may also have facility for receiv- References C'ted ing the manual controller to provide the annunciator UNITED STATES PATENTS system with plural inputs. units. In a preferred arrangement, the system shown in hospital usage 3,392,349 7/1968 Bartley ..340/244 C he e it rovides for the monitoring of a liquid level, 3,631,437 12/1971 Campbell ..340/244 C 17 Claims, 12 Drawing Figures CENTRAL REMOTE STATION I STATION 5 ,/2 1 /4 38 22 Qti fig SECONDARY jj CONTROLLER CURRENT ANNUNCIATOR 34 (FIGS.3A,3B) SOURCE UNIT i 24 (FIGS, 2A,2B) 2'? 44 3 I "-46 l I l 56 64 1 g VOLTAGE PRIMARY OSCILLATOR DETECTOR sENsmvE CONTROLLER 50 (FIG 5) (FIG 5) SWITCH l (FIGSAAAB) I (FIGS,6A,6B)

ANNUNCIATOR SYSTEM FIELD OF THE INVENTION This invention relates to annunciator systems and to improved condition detector apparatus for use therein.

BACKGROUND OF THE INVENTION The expansion of the capabilities of annunciator systems in existing installations is of substantial current interest. For instance, in presently constructed hospitals, the expansion of the capabilities of the customary patient call annunciator system to provide monitoring of various conditions, eg instantaneous liquid levels in intravenous feeding and body fluid collection, would provide evident advantages. Clearly, such additional annunciating capabilities would afford opportunities for a reduction in the number of personnel needed for customary periodic condition monitoring and for increased security inherent in continuous condition monitoring.

In the exemplary instance, i.e., expansion of the capabilities of the hospital patient call system, various considerations affect the practicality of expansion, and, if not satisfied, tend to overcome the above-discussed advantages. Typically, the patient call system comprises a central station having a current source and annunciator panel and plural remote stations, each including a patient-operated switch adapted to control current flow through its associated central station annunciator. Accordingly, a seemingly expeditious manner of system expansion is the provision of remote station condition detector apparatus adapted to operate the patient switch upon detection of a condition of predetermined interest and deriving its operating current from conductors other than those conducting annunciator controlling current. Such approach to system expansion is, however, greatly impractical since it necessitates elaborate mechanical apparatus for said patient switch operation and separate conductors providing detector apparatus operating current and does not enable central station discrimination as to whether the patient or the detector apparatus is responsible for the change in annunciator control current.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved annunciator system integrally incorporating a pre-existing annunciator system and expanding the annunciating capability thereof.

It is a more particular object of this invention to provide a hospital annunciator system combining at least an integral part of a pre-existing patient call annunciator system with condition detector apparatus deriving its operating current through such pre-existing system.

It is a further object of this invention to provide improved condition detector apparatus for use in th systems of the invention.

In the efficient attainment of these and other objects, the invention provides an annunciator system comprising a central annunciating station and a remote station, the remote station including a receptacle connected to the central station, and connector-adapter means matable with the receptacle and incorporating circuit means for both conveying annunciator control signals to the central station and conducting operating current from the central station through the receptacle to associated remote station condition detecting apparatus. The connector-adapter may further include the facility for receiving annunciator controllers normally matable with the remote station receptacle whereby the system is effective to provide annunciator control signals upon the occurrence of a detected condition of interest and/or another separate event.

In its preferred form, the system of the invention is adapted for hospital usage and includes a pre-existing patient call annunciator system having a central station and a remote station modified only to the extent that a connector-adapter and associated circuitry for condition detection and annunciator control is substituted for the patient call plug at the remote station receptacle. In this arrangement of the system, the condition detector is preferably adapted for detection of a liquid level of interest and derives its operating power through the remote station receptacle while providing liquid level announcements through the pre-existing annunciators. Where desired, the system may have the capacity for concurrent distinct announcement of patient demands for attention or the occurrence of a liquid level of interest.

The term pre-existing, employed above and elsewhere herein to describe systems which are improved bythe invention, is intended to embrace all systems whose annunciating capabilities are expanded by the invention, irrespective of whether such systems predate the invention.

In describing the manner in which the invention provides its improved systems, we set forth examples of two such pre-existing systems and indicate the imdescription of embodiments thereof shown in the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of the system of the invention.

FIGS. 2A and 2B illustrate types of annunciator units employable in practicing the invention. 7

FIGS. 3A and 3B illustrate manually operable controllers employable as secondary controller 16 in FIG. 1.

FIGS. 4A and 4B are schematic diagrams of controllers employable as primary controller 48 in FIG. 1.

FIG. 5 is a schematic diagram of oscillator 54 and detector 58 of FIG. 1.

FIGS. 6A and 6B are schematic diagrams of circuits employable as voltage-sensitive switch 66 of FIG. 1.

FIG. 7 is a schematic diagram of an-optional circuit adapted for use in the FIG. 1 system to provide concurrent distinct system announcements.

FIG. 8 illustrates a vessel for liquid containment and electrode arrangements for use in detecting liquid levels of interest.

Referring to FIG. 1, an annunciator system comprises a central station, typically the nurses station on each floor of a hospital, including a current source and a plurality of annunciator units 12, and a plurality of remote stations, i.e., patients bedsides, each of which is associated with a one of annunciator units 12. In systems preexisting the invention and in widespread use, a receptacle 14 at the remote station is directly connected to the central station and a plug-in controller 16 is matable with the receptacle. In such systems, controller 16 may be of the type 16a shown in FIG. 3A, incorporating a patient operable push-toclose (PTC) switch 18a. In this instance, annunciator unit 12a (FIG. 2A) is employed, comprising a lamp 20a series-connected in line 22. Alternatively, the controller may be of type 16b (FIG. 3B) incorporating a patient operable push-to-open (PTO) switch 18b. In this instance, annunciator unit 12b (FIG. 2B) is employed, comprising a lamp 20b connectable across lines 22 and 24 through contact 26 and contact arm 28. Coil 30 is energized when switch 18b is closed and contact arm 28 engages contact 32 as shown in the drawings. In operation of such pre-existing systems, annunciator unit 12 is energized upon the operation of switches 18a, 18b by a patient, thereby providing indication at the nurses station of his need for attention.

In accordance with the present invention, such preexisting system is modified by the introduction of a connector-adapter 38 (FIG. I) having a plug-in section matable with receptacle l4 and preferably a receptacle section matable with unit 16. The customary direct interconnection of patient switch 18 and its associated annunciator unit 12 is interrupted by circuitry connectable to connector-adapter 38. As illustrated, the plug-in section of unit 38 includes lines 40 and 42 respectively connectable with lines 34 and 36 and the receptacle section thereof may includelines 44 and 46 across which controller 16 may be connected. In this respect, it should be understood that the subject invention pertains to the illustrated system with controller 16 being optional and, to this extent, controller 16 is referred to hereinafter as a secondary controller. In use of the system of the invention with annunciator units 12a, secondary controller 16 may be omitted without any substitute connection to lines 44 and 46. Where annunciator units 12b are employed, in the absence of secondary controller 16 lines 44 and 46 may be interconnected by ajumper inserted into the receptacle section of connector-adapter 38.

Lines 40-46 are connected to primary controller 48, variant forms of which, 48a and 48b, are illustrated in FIGS. 4A and 48 respectively for use in systems employing annunciator units 12a and 12b. As discussed in detail'below, the primary controller constitutes circuit means adapted both to provide control of current flow through annunciator units 12 and, at the same time, to conduct operating current to detector apparatus. The controller 48 is also connected to lines 50 and 52, line 50 being directly connected to oscillator 54 and line 52 being connected to oscillator line 55. Oscillator 54 may oscillate in relation to the level of a liquid, e.g., a solution for intravenous feeding, and accordingly provides an output signal on line 56 connected to detector 58.

The detector is connected to controller 48 by lines 50 and 60 and by lines 52 and 62. An output signal of preselected amplitude is provided by detector 58 on line 64 upon the occurrence of a liquid level of interest and is applied to voltage-sensitive switch 66. This switch is connected to controller 48 by lines 50, 60 and 68 and by lines 52 and 70. Upon application of such preselected signal to switch 66, the switch provides an output signal on line 72 to primary controller 48. Controller 48 is responsive to this signal to control current flow through annunciator unit 12 to provide visible indication at the central station of the occurrence of the liquid level of interest. Such liquid level may be detected either in a liquid dispensing or liquid collection mode as discussed below.

Where secondary controller 16 is employed in conjunction with primary controller 48 and associated circuitry 50-72, primary controller circuit structure permits continuing control of annunciator unit 12 by the secondary controller. Thus, the secondary controller may be operated, as in said pre-existing systems, to provide central station annunciation of a patients demand for attention. Where desired, as discussed below in connection with FIG. 7, the system of the invention permits concurrent distinct indication of both such patient demand and the occurrence of a liquid level of interest. In addition, controller 48 circuit structure provides that all operating current for itself and units dependent thereon be derived from source 10 without need for modification of the pre-existing system.

In the following detailed discussion of the structure and operation of the systems of the invention, initial discussion is provided for the system embodiment employing annunciator unit 12a, primary controller 480, secondary controller 16a (optional) and voltage-sensitive switch 66a. The remaining elements of the system, e.g., current source 10, oscillator 54 and detector 58, are the same in each of the system embodiments.

In the first system embodiment of the invention, lamp 20a of annunciator unit 12a is series-connected between lines 22 and 34, lines 24 and 36 being directly interconnected. In such arrangement, current of nominal amplitude may be drawn through lamp 200 without exciting the lamp to provide a visible output. Applicants provide, to advantage discussed below, that the operating current for liquid level detection may readily be maintained below such nominal amplitude, e.g., by use of low current drain circuitry, thereby avoiding energization of lamp 20a,during quiescent conditions, namely, when either the liquid level of interest has not occurred or when the patient is not in need of attention.

Referring to FIG. 4A, primary controller 48a may include a rectifier 74 where current source 10 is an alternating current source. The rectifier is connected to lines 40 and 42 and provides its output on lines 76 and 78. Line 76 is directly connected to line 46 of adapterconnector 38 and is connected through resistor to connector-adapter line 44 through resistor 114. A Zener diode 82, or like device exhibiting a predetermined breakdown voltage is connected between line 78 and resistor 80 and provides a substantially constant direct current voltage across lines 50 and 52 which conduct operating current circuit to elements 54, 58 and 66 of FIG. 1. A voltage divider comprising resistors 84 and 86 is connected between lines 76 and 72 for biasing the base of transistor 88. The transistor emitter is directly connected to line 46 and the transistor collector is directly connected to the junction of resistor 80 and diode 82. A local indicator for the remote station, comprising a lamp 90 and diode 92, may be connected across lines 50 and 72 where desired.

Referring to FIG. 5, oscillator 54 may be of conventional structure, including transistors 94 and 96 and associated biasing and operating components. The base of transistor 96 is directly coupled to the collector of transistor 94 and the collector of transistor 96 is coupled through capacitor 98 to the base of transistor 94. Operating current is supplied to the oscillator by lines 50 and 55 and the oscillations thereof are controlled by capacitor 98. In a particularly preferred application of the invention, the electrodes of capacitor 98 are secured to the exterior of an intravenous liquid feeding vessel, the oscillator circuit elements being selected such that sustained oscillations accompany the presence of liquid intermediate the capacitor electrodes. Such sustained oscillations discontinue as the liquid recedes from such level.

During occurrence of sustained oscillations, transistor 100 of detector 58 (FIG. 5) conducts periodically, discharging capacitor 102. Upon cessation of oscillations, transistor 100 is rendered non-conductive and capacitor 102 charges toward line 50 voltage, i.e., detector output line 64 goes negative.

Voltage-sensitive switch 66a of FIG. 6A includes transistor 104, the base of which is directly connected to line 64. The collector of transistor 104 is directly connected to line 68 and the emitter thereof is connected through resistor 106, switch 108 and resistor 110 to line 70. The transistor is rendered conductive upon the occurrence of said negative voltage on line 64 and accordingly applies a negative voltage to the base of transistor 112, in turn rendering transistor 112 conductive. Line 72 is thereupon set at approximately the same voltage as line 70, i.e., positive.

Referring again to FIG. 4A, when line 72 is positive as discussed, a positive signal is thereby applied to the base of transistor 88, switching transistor 88 into conduction and short-circuiting resistor 80. This short-circuiting of resistor 80 increases the current drawn from rectifier 74 and hence from current source 10. By appropriate selection of component values, the current drawn on this event is increased far above said nominal amplitude to a level sufficient for energization of annunciator unit 12a.

In summary of the operation of the first system embodiment, it will be seen that the occurrence ofa liquid level of interest, e.g., intravenous feeding liquid decreasing to below a given level, gives rise to the cessation of sustained oscillations in oscillator 54, the detection of such cessation by detector 58, the closing of switch 66 and the further closing of switch 88 of primary controller 48a. Shunting of resistor 80 may also be accomplished by the closure of PTC switch 18a of secondary controller 16a, which provides continuity between lines 44 and 46 through resistor 114. Resistor 114 may be dispensed with, but when used, is selected to have a value such that its resistance sufficiently shunts resistor 80 to provide a current flow energizing lamp a. Thus, annunciator unit 12a may be energized either by the primary or the secondary controller.

In FIG. 6A, switch 108 is illustrated in the position labeled D (liquid dispensing). Where the collection of liquid to a preselected level in a vessel is ofinterest, this switch is placed on the C (liquid collection) position thereof. In this mode of operation, the start rather than the cessation of oscillation in oscillator 54 is detected. Prior to the commencement of oscillations, i.e., when liquid is not present between the electrodes of capacitor 98, line 64 of detector 58 is negative, back-biasing transistor 116 in turn back-biasing transistor 112. As oscillations commence, line 64 goes positive, switching transistor 116 into conduction. This, in turn, renders transistor 112 conductive, thereby providing a positive signal on line 72 and energizing annunciator unit 12a.

Where it is desired to provide selective indications at the central station of both the patients need for attention and the occurrence ofa liquid level of interest, the optional circuit means shown in FIG. 7 may be introduced in the above-discussed first embodiment of the invention. In FIG. 6A, optional dotted lines 118, 120 and 122 are provided for this purpose and interconnect with the circuit means of FIG. 7 as indicated. The FIG. 7 circuitry comprises a free-running multivib'rator including transistors 124 and 126 and associated resistors and capacitors connected in known manner to provide periodic output pulses on line 128. Transistor 130 is rendered conductive during occurrence of the pulses on line 128 and line 120 and accordingly is periodically connected to line 122 (positive potential). By use of this optional circuit means, the base of transistor 112 of voltage-sensitive switch 66a is periodically connected to a positive potential. When its base is connected to a positive potential, transistor 112 is rendered non-conductive, irrespective of the occurrence or non-occurrence ofa liquid level of interest. Assuming, by way of example, that line 64 indicates the occurrence of a liquid level of interest, rendering transistor 104 conductive, transistor 112 will be rendered alternately conductive and non-conductive during the occurrence of such liquid level of interest as determined by control of line 120 by the FIG. 7 circuit. Line 72 accordingly provides a periodic positive signal to transistor 88 of primary controller 480 with the result that transistor 88 is periodically switched into conduction and lamp 20a flashes at this frequency. Assuming further that patient switch 18a is continually closed during the occurrence of a liquid level of interest, resistor of the primary controller will be effectively short-circuited periodically by transistor 88 during conduction thereof and will be continually shunted by resistor 114. Evidently, the current conducted through annunciator unit will be at least at a first level determined by the shunting effect of resistor 114, sufficient to provide dull illumination of lamp 20a and, during periods of conduction of transistor 88, will be at a higher level, providing increased visible output in lamp 20a. A pulsating light output of lamp 20a overriding the constant glow will result, providing concurrent distinct indications of both the occurrence of the liquid level of interest and of the patients need for attention.

In a second embodiment of the invention, annunciator unit 12b is employed in conjunction with primary controller 48b (FIG. 4B), secondary controller 16b (optional) and voltage-sensitive switch 662; (FIG. 6B). Lines 44 and 46 are either connected together or to secondary controller 16b. in this system embodiment, a current of predetermined magnitude sufficient to energize coil 30 and maintaincontact arm 28 in engagement with contact 32 is required at all times other than upon the occurrence of either or both of a patient's demand for attention and a liquid level of interest. Where the current through annunciator unit 12b decreases below such predetermined magnitude, coil 30 is deenergized and contact arm 28 is spring-biased into engagement with contact 26 thereby energizing lamp 20b. The manner in which current flow through unit 1212 is controlled will be evident from a consideration of the detailed circuitry of primary controller 481: and

switch 66b.

Referring to FIG. 4B, controller 4812 has the same lines for interconnection with remaining elements of the system as in the case of controller 48a and incorporates various like elements including rectifier 74, resistor 80, zener diode 82, transistor 88 and biasing resistors 84 and 86. A remote station indicator 132 may be included where desired. Transistor 88 is again connected such that it effectively shunts resistor 80 when rendered conductive. n the other hand, lines 44 and 46, extending from the secondary controller, do not shunt resistor 80 but are connected respectively to line 72 and resistor 86. Switch 661: (FIG. 6B) incorporates the same circuit elements as in the case of switch 66a with the exception that switch 108 is oppositely poled, providing communication between transistors 104 and 112 in the liquid collection mode and providing communication between transistors 112 and IE6 in the dispensing mode.

For purposes of explanation, let it be assumed that patient switch 16b is in the position shown in FIG. 3b

(unoperated) and that liquid being collected has not reached a level of interest. Under these conditions, oscillator 54 is non-oscillating and detector 58 provides a negative potential on line 64 to which switch 66b responds with conduction occurring in both transistors 104 and 112. line 72 is accordingly positive and a positive potential is applied to the base of transistor 88 rendering this transistor conductive and shunting resistor 80. Current flow through annunciator unit 12b is accordingly of sufficient magnitude to maintain coil 30 energized and lamp 20b is unenergized. As oscillations commence upon the occurrence of the liquid level of interest, detector output line 64 goes positive whereupon transistors 104 and 112 are rendered non-conductive. Line 72 recedes from its positive level and transistor 88 is rendered non-conductive and the current therethrough is greatly reduced, thereby decreasing the loading of current source such that current flow through annunciator unit 12b decreases to a level insufficient for maintaining coil 30 energized with resulting energization of lamp b. Evidently, where switch 18b of secondary controller 16b is operated by conductive during oscillations and nonconductive upon occurrence of the liquid level of interest.

FIG. 8 illustrates a physical embodiment of capacitor 98 of oscillator 54 which is suitable for detection of liquid levels of solutions. The salinity of these solutions for hospital usage is frequently of appreciable magnitude, thereby providing a relatively conductive liquid. Accordingly, the liquid in conjunction with conductive strip electrodes 134 and 136 and the dielectric wall of the vessel, e.g., a glass or plastic container, provides a resistive-capacitive feedback path between oscillator lines 138 and 140. As the liquid level drops below the strip electrodes, conduction in the feedback path is substantially reduced, giving rise to the cessation of oscillations. Electrode strips 134 and 136 may be comprised of metallic strip material secured in opposing relation to the outer wall of the liquid containing vessel.

Where the salinity of the monitored liquid is appreciable, it is preferable to introduce a further electrode strip 142, secured to the vessel outer wall adjacent one of electrode strips 134 and 136. Electrode strip 142, when used, is connected by line 144 to oscillator 54 and, as indicated in FIG. 5, is connected in turn by line 55 to rectifier line 78. In operation of the system 1 incorporating electrode strips 134, 136 and 152, three capacitances are involved. First and second capacitances are defined as between the liquid and electrode strips 134 and 136 and a third capacitance exists as between electrode strip 142 and the liquid. The first and second capacitances are series connected by the liquid and the third capacitance is effectively a shunt capacitance connected intermediate the first and second capacitance to line 78. As liquid level drops below electrode strips 134 and 136, the third capacitance acts as a shunt and oscillations cease more rapidly. This arrangement is particularly effective where some adherence of the liquid to the interior walls of the vessel occurs for an interval following the receding of the liquid level below electrodes 134 and 136. In

this event, in the absence of electrode strip 142, a high resistance-low capacitance path may persist between lines 138 and 140. Absent the third shunt capacitance, this path may cause oscillation to persist for a slight time longer after the receding of the liquid to the level of interest.

In a practical usage of the systems of the invention, the patient call plug is removed from the remote station receptacle of a pre-existing annunciator'system and the connector-adapter of the invention is simply installed in the receptacle. All operating current for the controller and detector apparatus is provided through the connector-adapter and no ancillary connections are required, e.g., power cords at the patients bedside are not needed. If desired, the patient call plug may be inserted in the receptacle section of the connectoradapter and used by the patient while the detector apparatus is operative.

While the invention has been described in connection with the foregoing hospital related application and more particularly in connection with liquid level detection, the invention is clearly applicable to both expanding the capabilities of other pro-existing annunciator systems and to detection of conditions other than liquid level change. Moreover, the particularly disclosed embodiments of the system may be evidently modified by those skilled in the art without departing from the spirit of the invention and accordingly, the illustrated embodiments are intended in a descriptive and not in a limiting sense. The true scope of the invention is defined in the following claims.

What is claimed is:

1. An annunciator system comprising a central station including a current source and annunciator means connected thereto and a remote call station including a receptacle for connection to said annunciator means and plug-in means matable with said remote station receptacle, said plug-in means having a receptacle for call means and further comprising: detecting means for detecting the occurrence of a predetermined condition; signal generator means responsive to said detecting means for generating an output signal indicative of said condition occurrence; means conducting current from exclusively said receptacle to both said detecting means and said signal generator means for energization thereof; and control means operatively responsive to said signal generator output signal for controlling said current conducting means, thereby modifying current flow through said annunciator means to selectively energize said annunciator means to provide a sensible output upon the occurrence of said condition.

2. The system claimed in claim 1 wherein said current conducting means includes an impedance connected in series circuit with said annunciator means and wherein said control means includes a switch member connected in parallel with said impedance and operate: by said signal generator output signal.

3. The system claimed in claim 2 wherein said annunciator means is energized upon current flow therethrough of magnitude higher than a predetermined magnitude, said switch member being rendered conductive by said signal generator output signal and thereby increasing current flow to a magnitude higher than said predetermined magnitude.

4. The system claimed in claim 2 wherein said annunciator means is energized upon current flow therethrough of magnitude less than a predetermined magnitude, said switch member being rendered nonconductive by said signal generator output signal and thereby decreasing said current flow to a magnitude less than said predetermined magnitude.

5. The system claimed in claim 3 wherein said annunciator means includes a visible indicator having a filament connected in series circuit with said current source and said impedance.

6. The system claimed in claim 4 wherein said annunciator means includes a visible indicator having a filament connected through normally open contact means across said current source and further includes contact closure means connected in series circuit with said current source and said impedance.

7. The system claimed in claim 3 wherein said plug-in means includes a receptacle section adapted for connecting manually operable switch means in parallel with said impedance for selectively energizing said annunciator means upon operator input to said manually operable switch means.

8. The system claimed in claim 4 wherein said plug-in means includes a receptacle section adapted for connecting manually operable switch means in series circult with said control means for selectively energizing said annunciator means upon operator input to said manually operable switch means.

9. The system claimed in claim 7 wherein said manually-operable switch means includes a normally non-conductive switch element rendered conductive by said operator input.

10. The system claimed in claim 8 wherein said switch means includes a normally conductive switch element rendered non-conductive by said operator input.

11. The system claimed in claim 1 wherein said condition detecting apparatus includes an oscillator the frequency of oscillation of which exhibits preselected change upon the occurrence of said predetermined condition.

12. The system claimed in claim 11 wherein said predetermined condition is the occurrence of a preselected liquid level, said oscillator including a capacitance means having first and second electrodes adapted for securement in opposing coplanar relation to a dielectric vessel containing said liquid.

13. The system claimed in claim 12 wherein said capacitance means includes a third electrode adapted for securement to said vessel in non-coplanar relation to said first and second electrodes.

14. The system claimed in claim 8 wherein said signal generator generates a periodic output signal.

15. The system claimed in claim 11 whereinsaid predetermined condition is the occurrence of a preselected liquid level, said oscillator including a capacitance means having first and second electrodes adapted for securement to a dielectric vessel containing said liquid and defining there-with first and second series-connected capacitors, said vessel providing the dielectric for said capacitors.

16. The system claimed in claim 15 including a third capacitor comprising a third electrode and said liquid, said vessel providing the dielectric for said third capacitor, said third capacitor being connected to said first and second capacitors by said liquid.

17. Apparatus for use in an annunciator system having a central annunciating station including a current source and annunciating means and a remote receptacle connected to said station and adapted for receipt of a plug-in member manually operable to provide a control input to said annunciator system, said apparatus comprising an adapter-connector insertable in said receptacle for connection of said adapter-connector to said station and adapted for receipt of said plug-in member, and circuit means connected by said adapterconnector to said station, thereby deriving operating power from said current source, for providing a further control input to said annunciator system, said circuit means comprising detector means for detecting the occurrence of a predetermined condition, signal generator means operatively responsive to said detector means for generating an output signal indicative of said condition occurrence and control means operatively responsive to said signal generator means for providing said further control input to said annunciator system upon occurrence of said condition. 

1. An annunciator system comprising a central station including a current source and annunciator means connected thereto and a remote call station including a receptacle for connection to said annunciator means and plug-in means matable with said remote station receptacle, said plug-in means having a receptacle for call means and further comprising: detecting means for detecting the occurrence of a predetermined condition; signal generator means responsive to said detecting means for generating an output signal indicative of said condition occurrence; means conducting current from exclusively said receptacle to both said detecting means and said signal generator means for energization thereof; and control means operatively responsive to said signal generator output signal for controlling said current conducting means, thereby modifying current flow through said annunciator means to selectively energize said annunciator means to provide a sensible output upon the occurrence of said condition.
 2. The system claimed in claim 1 wherein said current conducting means includes an impedance connected in series circuit with said annunciator means and wherein said control means includes a switch member connected in parallel with said impedance and operated by said signal generator output signal.
 3. The system claimed in claim 2 wherein said annunciator means is energized upon current flow therethrough of magnitude higher than a predetermined magnitude, said switch member being rendered conductive by said signal generator output signal and thereby increasing current flow to a magnitude higher than said predetermined magnitude.
 4. The system claimed in claim 2 wherein said annunciator means is energized upon current flow therethrough of magnitude less than a predetermined magnitude, said switch member being rendered non-conductive by said signal generator output signal and thereby decreasing said current flow to a magnitude less than said predetermined magnitude.
 5. The system claimed in claim 3 wherein said annunciator means includes a visible indicator having a filament connected in series circuit with said current source and said impedance.
 6. The system claimed in claim 4 wherein said annunciator means includes a visible indicator having a filament connected through normally open contact means across said current source and further includes contact closure means connected in series circuit with said current source and said impedance.
 7. The system claimed in claim 3 wherein said plug-in means includes a receptacle section adapted for connecting manually operable switch means in parallel with said impedance for selectively energizing said annunciator means upon operator input to said manually operable switch means.
 8. The system claimed in claim 4 wherein said plug-in means includes a receptacle section adapted for connecting manually operable switch means in series circuit with said control means for selectively energizing said annunciator means upon operator input to said manually operable switch means.
 9. The system claimed in claim 7 wherein said manually-operable switch means includes a normally non-conductive switch element rendered conductive by said operator input.
 10. The system claimed in claim 8 wherein said switch means includes a normally conductive switch element rendered non-conductive by said operator input.
 11. The system claimed in claim 1 wherein said condition detecting apparatus includes an oscillator the frequency of oscillation of which exhibits preselected change upon the occurrence of said predetermined condition.
 12. The system claimed in claim 11 wherein said predetermined condition is the occurrence of a preselected liquid level, said oscillator including a capacitance means having first and second electrodes adapted for securement in opposing coplanar relation to a dielectric vessel containing said liquid.
 13. The system claimed in claim 12 wherein said capacitance means includes a third electrode adapted for securement to said vessel in non-coplanar relation to said first and second electrodes.
 14. The system claimed in claim 8 wherein said signal generator generates a periodic output signal.
 15. The system claimed in claim 11 wherein said predetermined condition is the occurrence of a preselected liquid level, said oscillator including a capacitance means having first and second electrodes adapted for securement to a dielectric vessel containing said liquid and defining there-with first and second series-connected capacitors, said vessel providing the dielectric for said capacitors.
 16. The system claimed in claim 15 including a third capacitor comprising a third electrode and said liquid, said vessel providing the dielectric for said third capacitor, said third capacitor being connected to said first and second capacitors by said liquid.
 17. Apparatus for use in an annunciator system having a central annunciating station including a current source and annunciating means and a remote receptacle connected to said station and adapted for receipt of a plug-in member manually operable to provide a control input to said annunciator system, said apparatus comprising an adapter-connector insertable in said receptacle for connection of said adapter-connector to said station and adapted for receipt of said plug-in member, and circuit means connected by said adapter-connector to said station, thereby deriving operating power from said current source, for providing a further control input to said annunciator system, said circuit means comprising detector means for detecting the occurrence of a predetermined condition, signal generator means operatively responsive to said detector means for generating an output signal indicative of said condition occurrence and control means operatively responsive to said signal generator means for providing said further control input to said annunciator system upon occurrence of said condition. 